Rubber composition for vibration isolating laminate body

ABSTRACT

PCT No. PCT/JP97/01503 Sec. 371 Date Oct. 8, 1998 Sec. 102(e) Date Oct. 8, 1998 PCT Filed May 1, 1997 PCT Pub. No. WO97/42265 PCT Pub. Date Nov. 13, 1997A rubber composition for base isolation laminates, comprising a natural rubber and/or an isoprene rubber, a polybutadiene rubber composite, a petroleum resin and fine particulate carbon black.

TECHNICAL FIELD

The present invention relates to a rubber composition for base isolationlaminates which can efficiently absorb vibration energy and is excellentin long-term endurance.

BACKGROUND ART

Various equipment for absorbing vibrational energy such as vibrationisolators, vibration dampers or seismic isolators have recently beenspread rapidly. Further, rubber compositions exhibiting a damping power(absorbing power) against vibrational energy are used in such equipment.

As means for imparting excellent damping characteristics to a rubbermaterial, i.e., obtaining a rubber composition having excellent dampingcharacteristics, it has been a common practice to add a large amount ofcarbon black or a petroleum resin to a rubber.

However, the addition of a large amount of carbon black haddisadvantages in that the resulting composition was poor inprocessability in refining and that the resulting seismic isolator waspoor in shear failure characteristics, though the resulting compositionexhibited an enhanced damping capacity (i.e., an enhanced hysteresisloss). On the other hand, the addition of a large amount of a petroleumresin had a disadvantage in that the resulting rubber compositionexhibited lowered creep characteristics and was poor in long-termendurance, though the composition was improved in dampingcharacteristics.

DISCLOSURE OF INVENTION

The present invention aims at providing a rubber composition for baseisolation laminates which is excellent in vibrational energy absorbingproperties and long-term endurance.

In order to attain this aim, the rubber composition for base isolationlaminates according to the present invention is characterized bycomprising 100 parts by weight of a rubber component comprising 90 to 50parts by weight of a natural rubber and/or an isoprene rubber and 10 to50 parts by weight of a polybutadiene rubber composite, 15 to 60 partsby weight of a petroleum resin and 50 to 90 parts by weight of fineparticulate carbon black, the polybutadiene rubber composite comprising97 to 80% by weight of a cis-1,4-polybutadiene rubber having acis-1,4-linkage content of 90% or above and 3 to 20% by weight of asyndiotactic 1,2-polybutadiene.

Such a combination of a natural rubber (NR) and/or an isoprene rubber(IR) with a polybutadiene rubber composite (BR composite), a petroleumresin and fine particulate carbon black makes it possible to obtain arubber composition improved in vibrational energy absorbing propertiesand long-term endurance.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a sectional view illustrating an example of the base isolationlaminate.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, a base isolation laminate 1 has a structure wherein aplurality of sheets of a rubber composition 2 are laminated with rigidhard plates 3 (e.g., steel sheets) sandwiched among the sheets.

The rubber composition of the present invention comprising a naturalrubber (NR) and/or an isoprene rubber (IR), a polybutadiene rubbercomposite (BR composite), a petroleum resin and fine particulate carbonblack is used as the rubber composition 2 shown in FIG. 1.

In the present invention, 100 parts by weight of a rubber componentcomprising 90 to 50 parts by weight of NR and/or IR and 10 to 50 partsby weight of the BR composite is blended with 15 to 60 parts by weightof a petroleum resin and 50 to 90 parts by weight of fine particulatecarbon black.

When the amount of NR and/or IR added exceeds 90 parts by weight, theresulting rubber composition will be poor in elongation, while when itis less than 50 parts by weight, the composition will be poor inprocessability and damping capacity. The term "NR and/or IR" used inthis description refers to the use of either NR or IR or that of both NRand IR.

The polybutadiene rubber composite (BR composite) comprises 97 to 80% byweight of a cis-1,4-polybutadiene rubber having a cis-1,4-linkagecontent of 90% or above and 3 to 20% by weight of a syndiotactic (syn)1,2-polybutadiene. The BR composition is commercially available, forexample, under the trade name of "UBEPOL-VCR" from Ube Industries, Ltd.

The term "petroleum resin" refers to a resin prepared by distilling aproduct of thermal cracking of petroleum naphtha to obtain a C₉ -C₁₀fraction containing polymerizable components such as indene andα-methylstyrene and subjecting this fraction to cationic polymerization.Such a resin is commercially available under the trade name of "FTR"(from Mitsui Petrochemical Industries, Ltd.), "Hiresin" (from TohoChemical Industry Co., Ltd.), "Cumarone resin" (from Nippon SteelChemical Co., Ltd.) or the like.

In the present invention, 15 to 60 parts by weight of a petroleum resinis blended with 100 parts by weight of the rubber component. When theamount of the petroleum resin is less than 15 parts by weight, theresulting composition will be poor in vibrational energy absorbingcapacity, while when it exceeds 60 parts by weight, the composition willbe poor in long-term endurance owing to its significant creep.

The fine particulate carbon black to be used in the present invention isone having a nitrogen specific surface area of 60 to 150 m² /g(preferably 80 to 150 m² /g) and a DBP absorption of 60 to 160 cm² /100g (preferably 90 to 160 cm² /100 g). Such a carbon black is commerciallyavailable as an HAF-, ISAF- or SAF-type one according to ASTM.

In order to obtain a rubber composition exhibiting an absorbing poweragainst vibrational energy, it is essential to add such a carbon black.The amount of the carbon black to be added is 50 to 90 parts by weightper 100 parts by weight of the rubber component. When the amount is lessthan 50 parts by weight, the resulting composition will be poor in theabsorbing capacity against vibrational energy, while when it exceeds 90parts by weight, the processability in preparing the rubber compositionwill be so poor as to give a rubber composition lowered in strengths.

In preparing the rubber composition of the present invention, avulcanization acceleration such as N-t-butyl-2-benzothiazolylsulfenamideand a vulcanization auxiliary such as zinc oxide or stearic acid may beadded to an unvulcanized rubber in proper amounts for the purpose of thevulcanization of the rubber.

FIG. 1 shows an example of the base isolation laminate wherein therubber composition of the present invention is used. As shown in FIG. 1,the base isolation laminate is constituted of sheets of the rubbercomposition 2 and hard plates 3 (such as general structural steel sheetsor cold rolled steel sheets) which are alternately laminated. The baseisolation laminate can be produced by molding and vulcanizing anunvulcanized rubber composition to obtain vulcanized rubber sheets andbonding the sheets to the hard plates with an adhesive. Alternatively,it can be produced by molding an unvulcanized rubber composition intosheets, laminating the sheets and the hard plates and heating theresulting laminate to conduct the vulcanization and bonding of thelaminate simultaneously.

The base isolation laminate according to the present invention is usefulas the support of a road bridge or the foundation support of a building.

EXAMPLES AND COMPARATIVE EXAMPLES

Rubber compositions were prepared according to the formulations (partsby weight) specified in Table 2 (Examples 1 to 6 and ComparativeExamples 1 to 5). The compositions were evaluated for tensile strength(T_(B)), elongation at break (E_(B)) and JIS A hardness (H_(S))according to the methods which will be described. As shown in FIG. 1,base isolation laminates (135 mm×135 mm×74 mm) were each produced byalternately laminating sheets of each rubber composition and steelsheets, and evaluated for equivalent damping constant (h), compressivecreep (%) and shear failure characteristics (%). The results are givenin Table 2.

Tensile Strength (T_(B), kgf/cm²)

The tensile strength of each rubber composition was determined accordingto JIS K 6301. A larger value means a higher strength and lowerliability to break.

Elongation at Break (E_(B), %)

The elongation at break of each rubber composition was determinedaccording to JIS K 6301.

Equivalent Damping Constant (h)

The equivalent damping constant of each base isolation laminate wasdetermined by the use of a biaxial shear testing machine at 0.1 Hz and astrain of 175%.

A high-damping rubber support to be used as the seismic isolator of abridge is required to exhibit such an energy absorbing power duringearthquake as to attain a damping constant expected in the design of thebridge. The correction factors of design horizontal seismic coefficientsbased on the damping constants of bridges are stipulated in "DesignManual of Base Isolation for Road Bridges" (Ministry of Construction,Public Works Research Center (foundation)), which is a basic designguide of base isolation. They are as given in Table 1.

                  TABLE 1                                                         ______________________________________                                                     Damping const.                                                                          Correction                                                          of bridge factor                                                 ______________________________________                                        Seismic        h < 0.1     1.0                                                coefficient    h ≧ 0.1                                                                            0.9                                                method                                                                        Horizontal load-                                                                             h < 0.1     1.0                                                carrying        0.1 ≦ h < 0.12                                                                    0.9                                                capacity method                                                                              0.12 ≦ h < 0.15                                                                    0.8                                                               h ≧ 0.15                                                                           0.7                                                ______________________________________                                    

Since the equivalent damping constant of a high-damping rubber supporttends to lower with increasing shear strain, it is appropriate that thedamping constant of a bridge as expected on the level of theload-carrying capacity method is 0.12 to 0.15. In order to satisfy thisappropriate damping constant, the equivalent damping constant of ahigh-damping rubber support on the level of strain of an object must beabout 0.13 or above.

Compressive Creep (%)

A creep which will occur during the design durable period was calculatedfrom the formula (1) based on the vertical displacement of a seismicisolator as caused by applying a vertical load corresponding to a designbearing stress of 60 kgf/cm² at +20° C. for 1000 hours.

    δ.sub.CR =at.sup.b                                   (1)

wherein

δ_(CR) : creep (mm) of a seismic isolator

t: design durable period (h) of a bridge

a, b: creep constants calculated by the equations (2) and (3):

    a=(δ.sub.100).sup.2 /(δ.sub.1000).sup.2        (2)

    b=log (δ.sub.1000 /δ.sub.100)                  (3)

δ₁₀₀ : vertical displacement (mm) of a seismic isolator after 100 hours

δ₁₀₀₀ : vertical displacement (mm) of a seismic isolator after 1000hours

It is necessary that the creep which will occur during the designdurable period of a bridge is at most 5% of the total thickness of therubber as calculated by the above formula (1).

Shear Failure Characteristics (%)

The shear modulus of each base isolation laminate was determined byapplying a shear load to the laminate in the vertical direction at arate of 0.5 mm/sec by the use of a biaxial shear testing machine under aload of 60 kgf/cm² to determine the shear modulus at break. It issuitable that the base isolation laminate has a shear modulus of 400% orabove.

                                      TABLE 2                                     __________________________________________________________________________                   Target                                                                            Comp.                                                                             Comp.                   Comp.                                                                             Comp.   Comp.                             Value                                                                             Ex. 1                                                                             Ex. 2                                                                             Ex. 1                                                                             Ex. 2                                                                             Ex. 3                                                                             Ex. 4                                                                             Ex. 5                                                                             Ex. 3                                                                             Ex. 4                                                                             Ex.                                                                               Ex.                __________________________________________________________________________                                                               5                  NR                 100  70  90  70  50  70  70  70  70  70  70                BR                      30                                                    VCR*.sup.1                  10  30  50  30  30  30  30  30  30                carbon black (ISAF)                                                                               85  85  85  85  85  85  85  85  85  60  40                petroleum resin (cumarone resin)                                                                  35  35  35  35  35  20  45  10  65  35  35                zinc oxide         5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0                stearic acid       1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                age resister       3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0                sulfur             2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1                vulcanization accelerator CZ                                                                     1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2                Basic Physical Properties:                                                    T.sub.B (kgf/cm.sup.2)                                                                           223 190 198 195 196 213 183 225 154 216 213                E.sub.B (%)        340 510 470 450 450 410 530 360 650 550 580                H.sub.S (JIS-A)     85  81  85  84  84  82  85  80  87  80  72                Characteristics as Seismic                                                    Isolator:                                                                     h              ≧0.13                                                                       0.14                                                                              0.12                                                                              0.14                                                                              0.14                                                                              0.135                                                                             0.13                                                                              0.145                                                                             0.125                                                                             0.155                                                                             0.13                                                                              0.115             compressive creep (%)                                                                         ≦5%                                                                       1.8 2   2.1 2.3 2.5 1.8 3.3 1.7 5.2 1.9 1.5                shear failure characteristic (%)                                                             ≧400%                                                                      370 450 430 430 420 410 450 400 480 460 470                __________________________________________________________________________     Note:                                                                         *.sup.1 VCR 412 (a product of Ube Industries, Ltd.), comprising               cis1,4-polybutadiene and syndiotactic 1,2polybutadiene at a weight ratio      of 88 to 12 and having a Mooney viscosity (ML.sub.1+4 (100° C.)) o     45.                                                                      

As apparent from the results given in Table 2, the composition ofComparative Example 1 which contained only a natural rubber (NR) as therubber component was poor in shear failure characteristics, while thecomposition of Comparative Example 2 which contained a natural rubber(NR) and a butadiene rubber (BR) as the rubber component, that ofComparative Example 3 which contained the petroleum resin in too smallan amount and that of Comparative Example 5 which contained carbon blackin too small an amount exhibited low equivalent damping constants (h)respectively and were poor in vibrational energy absorbing properties.Further, the composition of Comparative Example 4 which contained thepetroleum resin in too large an amount exhibited such a high compressivecreep (e) as to be poor in long-term endurance. Thus, it can beunderstood that the rubber compositions of Examples 1 to 6 according tothe present invention are superior to those of Comparative Examples 1 to5 in vibrational energy absorbing properties and long-term endurance.

As described above, the rubber composition for base isolation laminatesaccording to the present invention comprises 100 parts by weight of arubber component comprising 90 to 50 parts by weight of a natural rubberand/or an isoprene rubber and 10 to 50 parts by weight of apolybutadiene rubber composite, 15 to 60 parts by weight of a petroleumresin and 50 to 90 parts by weight of fine particulate carbon black, thepolybutadiene rubber composite comprising 97 to 80% by weight of acis-1,4-polybutadiene rubber having a cis-1,4-linkage content of 90% orabove and 3 to 20% by weight of a syndiotactic 1,2-polybutadiene. Byvirtue of this constitution, the rubber composition is excellent invibrational energy absorbing properties and long-term endurance.

What is claimed is:
 1. A rubber composition for base isolationlaminates, which rubber composition comprises(1) 100 parts by weight ofa rubber component comprising(a) 90 to 50 parts by weight of a naturalrubber and/or an isoprene rubber, and (b) 10 to 50 parts by weight of apolybutadiene rubber composite, (2) 15 to 60 parts by weight of apetroleum resin and (3) 50 to 90 parts by weight of fine particulatecarbon black,wherein the polybutadiene rubber composite comprises (i) 97to 80% by weight of a cis-1,4-polybutadiene rubber having acis-1,4-linkage content of at least 90% and (ii) 3 to 20% by weight of asyndiotactic 1,2-polybutadiene.
 2. The rubber composition for baseisolation laminates as set forth in claim 1, wherein the fineparticulate carbon black has a nitrogen specific surface area of 60 to150 m² /g and a DBP absorption of 60 to 160 cm³ /100 g.